1. Field of the Invention
This invention relates to an adhesive for electroless plating and a method of producing the same, and more particularly to an adhesive for electroless plating, which does not cause accidents such as dust explosion and the like in the production and exhibits an excellent interlaminar insulating property when being applied to the production of multilayer printed wiring boards, as well as a method of producing the same.
2. Description of Background Information
Recently, the printed wiring board or the wiring board mounting LSI are demanded to have a high densification of pattern and an improved reliability in correspondence with the miniaturization and high performance of electron parts with the advance of electron industry. For this end, there are lately noticed additive method and semi-additive method wherein an adhesive is applied onto a surface of a substrate to form an adhesive layer and the surface of the adhesive layer is roughened and subjected to an electroless plating to from a conductor circuit as a method of forming the conductor circuit on a wiring board.
For example, the formation of the wiring board by the additive method has a characteristic that the wiring can be produced at a high density and a low cost with a high pattern accuracy as compared with an etched foil method (subtractive method) conducting the pattern formation through etching because the conductor circuit is formed by subjecting to the electroless plating after the formation of a resist.
As the adhesive used in the above electroless plating, there is disclosed a photosensitive adhesive for electroless plating obtained by dispersing fine powder of heat resistant resin into a photosensitive resin matrix in JP-A-61-276875, JP-A-2-188992, U.S. Pat. No. 5,055,321 and the like. When such an adhesive for electroless plating is used to produce a multilayer printed wiring board, there is adopted a method wherein the surface of the adhesive layer is roughened with an oxidizing agent to selectively dissolve and remove only the fine powder of the heat resistant resin and thereafter the roughened surface is subjected to an electroless plating treatment, whereby it is made possible to produce multilayer printed wiring boards having a high peel strength of conductor.
When the adhesive for electroless plating dispersing the heat resistant resin particles is produced by the well-known method, it is usual to mix the uncured resin matrix with the cured heat-resistant resin particles and knead them through three-rollers.
Since the heat resistant resin particles are powder form, they stir up in air during the production or in the handling such as transportation, mixing or the like, so that there is a risk of causing dust explosion.
Even if it is intended to directly mix the above finer powder with the heat resistant resin matrix, the particles themselves are aggregated due to drying, so that such aggregated particles can not completely be disentangled by kneading. If the aggregated particle remains in the adhesive layer for electroless plating, when the portion of the aggregated particle is dissolved and removed by the roughening treatment, a big hole is formed in the adhesive layer for electroless plating. Particularly, when such an adhesive layer for electroless plating is used as an interlaminar insulating layer having a big hole, there is caused a fatal problem that upperlayer conductor circuit and underlayer conductor circuit are electrically connected to each other by the electroless plating to bring about poor insulation.
It is, therefore, an object of the invention to propose an adhesive for electroless plating causing no accident such as dust explosion or the like in the production as well as a method of producing the same.
It is another object of the invention to propose an adhesive for electroless plating advantageously used for the production of additive or semi-additive multilayer printed wiring board having an interlaminar insulating property as well as a method of producing the same.
The inventors have made various studies in order to achieve the above objects and as a result, the invention has been accomplished as the following constructions.
That is, the adhesive for electroless plating according to the invention is an adhesive for electroless plating obtained by dispersing cured particles of heat resistant resin soluble or decomposable in an acid or an oxidizing agent into an organic solvent to form a dispersion and mixing with an uncured resin, characterized in that the dispersion of the cured particles of the heat resistant resin in the organic solvent is obtained by dispersing cured particles formed in the production of heat resistant resin cured particles into the organic solvent without drying, and the uncured resin is a resin becoming hardly soluble in an acid or an oxidizing agent through curing treatment and capable of forming a heat resistant cured resin.
And also, the production method of the adhesive for electroless plating according to the invention is characterized in that an aqueous dispersion of cured particles obtained in the production of heat resistant resin cured particles soluble or decomposable in an acid or an oxidizing agent is subjected to a solvent substitution with an organic solvent without drying, and the resulting organic solvent dispersion of the cured particles obtained by the substitution is mixed with an uncured resin becoming hardly soluble in an acid or an oxidizing agent and converting into a heat resistant cured resin through a curing treatment to obtain an adhesive for electroless plating having a structure that the cured particles of the heat resistant resin are dispersed into the uncured resin and the organic solvent.
Furthermore, the production method of the adhesive for electroless plating according to the invention is characterized in that an aqueous dispersion of cured particles obtained in the production of heat resistant resin cured particles soluble or decomposable in an acid or an oxidizing agent is subjected to a solvent substitution with an organic solvent without drying, and the resulting organic solvent dispersion of the cured particles obtained by the substitution is mixed with an uncured resin becoming hardly soluble in an acid or an oxidizing agent and converting into a heat resistant cured resin through a curing treatment and a heat resistant thermoplastic resin to obtain an adhesive for electroless plating having a structure that the cured particles of the heat resistant resin are dispersed into the uncured resin, the heat resistant thermoplastic resin and the organic solvent.